Sieve cloth and method of using same

ABSTRACT

A method of controlling separation of solid particles from a fluid is described, wherein the separation is carried out by means of a sieve apparatus ( 10 ) which includes an endless sieve cloth ( 1 ) structured in a manner allowing it to rotate around at least two spaced-apart turning rollers ( 14 ), wherein the method comprises: arranging at least two sieve cloth sheets ( 1 ′) in series in the direction of movement of the sieve cloth ( 1 ), wherein at least two of the at least two sieve cloth sheets ( 1 ′) have dissimilar filtering characteristics; controlling the endless sieve cloth ( 1 ) by rotating the turning rollers ( 14 ) in such a manner that a desirable amount of solid particles and fluid is supplied to at least one of, or is distributed between two or more of, the at least two sieve cloth sheets having desirable filtering characteristics. A sieve cloth for use in the method is also described.

The present invention concerns a sieve cloth for operation in a sieve apparatus. More particularly, it concerns a sieve cloth for operation in a sieve apparatus in order to separate solid particles from a fluid, wherein the sieve apparatus is of a type provided with an endless sieve cloth structured in a manner allowing it to be moved around two spaced-apart turning rollers, and about a method of controlling separation of solid particles from a fluid.

The present invention is especially directed towards recovery of drilling mud which, together with drill cuttings, are brought up to a surface in context of drilling petroleum wells. It should be appreciated, however, that the invention also may be used for the purpose of separating fluids from solid particles other than drill cuttings.

Separation of solid particles from fluid flows by virtue of passing a fluid through a filtering- or sieving device having perforations of such a size that the solid particles are retained on the sieve surface instead of passing through it, represents well-known technology.

The present applicant has developed and put into production a sieve apparatus being sold under the trademark MudCube®. The sieve apparatus is based on an endless sieve cloth which, in operation, rotates around two spaced-apart turning rollers. A sieve apparatus of the endless sieve cloth type has proven to exhibit several advantages with respect to stationary sieve cloths being used in a vibratory sieve apparatus or a so-called “shale-shaker”. The advantages relate to, among other things, environmental, economic and capacity-related conditions as set forth in applicant's patent NO 323519.

The applicant describes, in his patent NO 325804, an apparatus and a method for guiding the movement of at least one endless sieve cloth which is structured in a manner allowing it to be moved around at least two spaced-apart turning rollers. The movement is guided by virtue of two or more portions of the sieve cloth being in engagement with at least one guiding device extending between the turning rollers of the sieve apparatus, and in such a manner that at least portions of the sieve cloth essentially are prevented from being able to move relative to the guiding device in a direction perpendicular to the direction of rotation of the sieve cloth. In one embodiment according to said NO 325804, the guiding device involves fixing the sieve cloth to a support belt which provides support to the sieve cloth between the turning rollers.

It has turned out, however, that a sieve cloth being attached to an underlying support belt is subject to undesirable loads capable of reducing the effective life of the cloth and, moreover, that it is relatively time-consuming to attach the sieve cloth to the guiding device. Among other things, the undesirable loads are due to the sieve cloth, which is disposed on the outside of the support belt, being forced to move at the same velocity as the support belt which is stretched between the turning rollers, despite the path of motion of the sieve cloth being longer than the path of motion of the support belt. Also, the applicant has carried out tests in which several individual cloths were fixed in series onto the support belt, however without observing improvements with respect to the above-mentioned disadvantages.

In Norwegian patent application No. 20110938, from which the present application is divided, a device and a method of connecting a sieve cloth in a sieve apparatus are described. The sieve cloth is capable of moving at a different velocity than that of an underlying support belt structured in a manner allowing it to support the sieve cloth between at least two spaced-apart turning rollers. Further, a simple and fast way of connecting or removing the sieve cloth to/from the apparatus is described.

Hereinafter, Norwegian patent application No. 20110938 will also be termed a “parent application”.

Upon recovery of e.g. drilling mud, however not limited thereto, it is desirable or required for the mud to satisfy specific properties with respect to, among other things, specific gravity and a grading curve for the material fines being admitted through the sieve cloth. Upon monitoring the properties of the drilling mud recovered by means of a sieve apparatus, the distribution of e.g. the fines content in the drilling mud may be adjusted so as to optimize the sieving operation without having to remove the sieve cloth from the sieve apparatus in order to replace it with a new one having a different filtering characteristic, as is done according to prior art.

From publication U.S. Pat. No. 2,220,985 A1, a sieve machine having an endless, perforated belt is known. When in operation, the belt is deformed widthwise so as to change the form of the perforations in the longitudinal direction of the belt.

From publication U.S. Pat. No. 5,887,729 A1, a sieve machine is known, wherein a plurality of endless sieve cloths having different filtering characteristics are disposed within each other.

Accordingly, the object of the invention is to remedy or to reduce at least one of the disadvantages of the prior art, or at least to provide a useful alternative to the prior art.

The object is achieved by virtue of features disclosed in the following description and in the subsequent claims.

According to a first aspect of the present invention, a method of controlling separation of solid particles from a fluid is provided, wherein the separation is carried out by means of a sieve apparatus which includes an endless sieve cloth structured in a manner allowing it to rotate around at least two spaced-apart turning rollers, wherein the method comprises:

-   -   arranging at least two sieve cloth sheets in series in the         direction of movement of the sieve cloth, wherein at least two         of the at least two sieve cloth sheets have dissimilar filtering         characteristics;     -   controlling the endless sieve cloth by rotating the turning         rollers in such a manner that a desirable amount of solid         particles and fluid is supplied to at least one of, or is         distributed between two or more of, the at least two sieve cloth         sheets having desirable filtering characteristics.

The effect thereof is that the distribution of the fines content in the drilling mud may be adjusted so as to optimize the sieving operation without having to remove the sieve cloth from the sieve apparatus in order to replace it with a new one having a different filtering characteristic. This is achieved by allowing the or those of the sieve cloth sheets having a desirable filtering characteristic, i.e. desirable filtering properties, to receive the material to be sieved, and allowing this or these sieve cloth sheets to undergo a back-and-forth motion, instead of allowing the endless sieve cloth to rotate in one direction only in the sieve apparatus. Optionally, the sieve cloth may be moved in one direction, but upon adjusting the velocity in accordance with the particular sieve cloth sheet receiving the material, the sieving operation may be optimized.

To facilitate the control of the movement of the sieve cloth, the method may further comprise providing the sieve cloth sheets with a signal transmitter structured in a manner allowing it to communicate with a receiver being connected to a control system. The control system is structured in a manner allowing it to control a driving device for rotation of at least one of the turning rollers.

Such a control system may also prove advantageous when a desirable portion of the sieve cloth is to be brought to a stop in a predetermined position in the sieve apparatus.

In one embodiment, the sieve cloth sheets extend across the entire width of the sieve apparatus, i.e. across most of the extent in the longitudinal direction of the turning rollers. In another embodiment, two or more sheets of sieve cloth are disposed in parallel. Advantageously, the two or more sheets of sieve cloth disposed in parallel are brought into engagement with each other in the adjoining side portions of the sheets. Said adjoining side portions may, but do not have to, extend parallel to the direction of movement of the sieve cloth.

The at least two sieve cloth sheets being arranged in series in the direction of movement of the sieve cloth, wherein at least two of the at least two sieve cloth sheets have dissimilar filtering characteristics, may be connected to a support belt by means of the following method:

-   -   bringing at least a portion of at least one of the sieve cloth         sheets into engagement with a portion of the support belt;     -   positioning the sieve cloth sheet against the support belt by         moving the support belt around the turning rollers; and     -   bringing at least two adjoining end portions of the sieve cloth         sheets into engagement with each other until the at least two         sieve cloth sheets form an endless sieve cloth.

In one embodiment, the method further comprises releasing the sieve cloth from said engagement with the support belt.

As such, the method according to the parent application may also be used for the present application.

In one embodiment, the end portions of at least one of the at least one sieve cloth sheet may be provided with a cloth attachment means at both the lower side and the upper side of the sieve cloth sheet. The effect thereof is that two or more sieve cloth layers may be disposed in layers, whereby the filtering characteristic and/or the effective life properties of the sieve cloth sheet may be changed.

The step of releasing the sieve cloth from engagement with the support belt may be an active step carried out by, for example, an operator. Alternatively, it may be a step occurring upon providing a relatively weak engagement between the sieve cloth and the support belt, and in such a manner that the engagement is broken by “shear stresses” arising when at least one of the turning rollers is set into rotation by means of a driving device, whereby the support belt and the endless sieve cloth disposed thereon are moved, however at a dissimilar velocity, as explained above.

Engagement between the sieve cloth and the support belt may be provided by means of an attachment means releasably connected to a portion of the support belt. The advantageous effect thereof is that the attachment means is connected to a desirable portion of the support belt without requiring the support belt to move, as would be the case if the attachment means was fixedly connected to the support belt. Another advantageous effect thereof may be that the attachment means may be removed from the support belt once the sieve cloth has been “threaded onto” the support belt. This, however, requires an active step on behalf of an operator.

In order to facilitate control of the apparatus, and especially remote control of the apparatus to reduce the risk of damage to operators, among other things, the method may further comprise connecting at least one first signal transmitter to a portion of the support belt; putting the at least one first signal transmitter into communication with a receiver connected to a control system, wherein the control system is structured to control a driving device providing rotation of the support belt, and in such a manner that the driving device is brought to a stop when the first signal transmitter is located in a predetermined position in the sieve apparatus.

The advantageous effect thereof is, among other things, that e.g. an attachment means fixedly connected to the support belt may be brought to a stop when in a favourable position for attaching at least one of the sieve cloth sheets in context of mounting thereof.

For example, the signal transmitter may be of a type described in applicant's so Norwegian patent application 20110438 and attached to the support belt by means of e.g. a clip device.

Correspondingly, and as mentioned, the method may further comprise connecting at least one second signal transmitter to a portion of the sieve cloth, and putting the at least one second signal transmitter into communication with a receiver connected to a control system, wherein the control system is structured in a manner allowing it to control a driving device providing rotation of the sieve cloth, possibly the support belt, and in such a manner that the interconnected end portions of the sieve cloth are brought to a stop in a predetermined position in the sieve apparatus. The control system may be, but does not have to be, the same as the above-mentioned control system which receives signals received from the receiver connected to the signal transmitter for a possible support belt.

For example, the effect thereof may be that the splice portion of the sieve cloth or the joining portion between two end portions may be brought to a stop when in a favourable position to the operator.

In a second aspect of the present invention, a sieve cloth is provided for operation in a sieve apparatus in order to separate solid particles from a fluid, wherein the sieve apparatus is of a type provided with an endless sieve cloth structured in a manner allowing it to be moved around two spaced-apart turning rollers, wherein the sieve is cloth comprises at least two sieve cloth sheets arranged in series in the direction of movement of the sieve cloth, and wherein at least two of the at least two sieve cloth sheets have dissimilar filtering characteristics.

The at least two sieve cloth sheets may be arranged as an endless sieve cloth prior to disposing it in a sieve apparatus. In so doing, however, the sieve cloth must be threaded inwards and onto the turning rollers from one side of the sieve apparatus. In a preferred embodiment, the sieve cloth sheets are attached to each other before or in the process of introducing the sieve cloth into the sieve apparatus, for example in accordance with the method of the parent application, as cited above.

By so doing, the at least two sieve cloth sheets may be connected to an endless sieve cloth.

At least one of the sieve cloth sheets may have a square shape with a width being equal to a length. The effect thereof is that the sieve cloth sheet may be rotated 90° relative to the direction of rotation or movement of the sieve cloth. The purpose of such a rotation is, among other things, to be able to change the filtering characteristic so of a sieve cloth sheet, wherein a size, in a longitudinal direction, of at least some of the openings of the cloth is dissimilar to the size, in a widthwise direction, of at least some of the openings of the cloth, as would be the case for openings having, for example, a rectangular shape.

In order to increase the effective sieve area of a sieve cloth sheet, the surface area of the sieve cloth sheet may be larger than a basic outline of the sieve cloth sheet, the outline of which is defined by the extent of the cloth in a longitudinal direction and in a widthwise direction. For example, such an increased sieve area may be achieved by providing a sieve cloth sheet provided with for example, but not limited thereto, a waveform, or with a plurality of restricted protrusions. In one embodiment, such a restricted protrusion is formed as a dome or a pyramid.

In one embodiment, at least one of the sieve cloth sheets may be provided with dividing profiles which, in operation, protrude upwards from a portion of the sieve cloth sheet. One of the objectives of the dividing profiles is to be able to provide a sieve chamber or sieve vessel structured to reduce lateral flow of material being supplied to the sieve cloth sheet.

At least those of the dividing profiles being non-parallel to the turning rollers are structured in a manner allowing them to be passed around the turning rollers in the sieve apparatus. In one embodiment, such dividing profiles are provided in a flexible material. Alternatively or additionally, the dividing profiles are provided with a plurality of slots allowing the dividing profiles to be bent around the turning rollers. Those of the dividing profiles possibly being arranged parallel to the turning rollers may, if desirable, be provided in a stiff material.

A support belt which may be disposed endlessly around the turning rollers of the sieve apparatus, may support the at least two sheets of sieve cloth.

The at least two sheets of sieve cloth may be provided with an engagement means structured to go into engagement with the support belt, as disclosed in the parent application.

In its simplest form, the engagement means may be comprised of a connection means, for example a rope or a strip inserted through e.g. loops/eyes arranged in the first end portion of the sieve cloth, the rope/strip of which is connected to the support belt.

Alternatively, the support belt may be provided with a second engagement means arranged within, or connected to, a portion of the support belt, for example, but not limited to, a hook device, a clamp, or a hinge lock.

Connecting the series of said at least two sieve cloth sheets to the support belt has the effect of allowing the sieve cloth to be threaded or passed over most of the support belt, and in such a manner that the at least two sieve cloth sheets may be connected together so as to form an endless sieve cloth.

The engagement means may be comprised of one of the first cloth attachment means and the second cloth attachment means. Upon having threaded or passed the sieve cloth over most of the support belt, the engagement means may thus be used as an attachment means in order to form the endless sieve cloth.

Engagement between two adjoining end portions of the sieve cloth may be provided by means of an attachment means which, for example, is chosen from a group consisting of: a zipper; a snap lock; hook and loop fasteners; one or more magnets; a series of push buttons, or any combination thereof; or an adhesive provided by means of a gluing agent or a vulcanization. For example, said one or more magnets may be comprised of a magnet strip- or list, or of a series of magnets.

Typically, a possible support belt is formed from support strings extending in a cross pattern, for example, but having a larger mesh aperture than the sieve cloth it is to support.

The sieve apparatus employing a sieve cloth according to the second aspect and the associated features is very suitable for use on a drilling rig to be used in context of drilling a well for recovery of petroleum, at which location there is a need for a simple way of being able to adjust the characteristic of the sieve apparatus.

Hereinafter, an example of a preferred embodiment is described and is depicted in the accompanying drawings, where:

FIG. 1 shows, in perspective, a front elevation of a sieve apparatus provided with at rotating sieve device;

FIG. 2 shows, in larger scale and in perspective, a front elevation of detail A;

FIG. 3 shows a side view of a portion of the sieve apparatus in FIG. 1, wherein an end portion of a sheet of sieve cloth is attached to a support belt;

FIG. 4 shows, in larger scale, detail B of FIG. 3;

FIG. 5 shows a plane view of an endless support belt, wherein a portion of a sheet of sieve cloth is brought into engagement with the support belt, and in a manner corresponding to that shown in FIG. 3;

FIG. 6 shows the same as in FIG. 3, but wherein a substantial part of the sheet of sieve cloth is positioned against the support belt;

FIG. 7 shows the same as in FIG. 5, but wherein the end portions of the sheet of sieve cloth are brought into engagement with each other, whereby the sheet of sieve cloth forms an endless sieve cloth;

FIGS. 8 a-8 b show plane views of three and two sheets, respectively, of sieve cloths brought into engagement with each other in a series;

FIG. 9 a shows, in perspective, a front elevation of two sheets of sieve cloth joined together, and wherein one of the sheets has a waveform, and wherein one of the sheets is provided with surrounding dividing profiles;

FIG. 9 b shows, in larger scale, detail C shown in FIG. 9 a;

FIG. 10 a shows, in perspective, a front elevation of an alternative embodiment of the sieve cloth sheet shown in FIGS. 9 a and 9 b; and

FIG. 10 b shows, in larger scale, detail D shown in FIG. 10 a.

Positional references, such as above, below, right and left, refer to the position shown in the relevant figure.

Equal or corresponding elements are denoted with the same reference numeral in the various figures.

In the figures, reference numeral 1 denotes a sieve cloth according to the present invention. The sieve cloth 1 may be comprised of two or more sheets 1′ which, when operational, are connected together so as to form an endless sieve cloth 1 for use in a sieve apparatus 10 of a type wherein the sieve cloth 1 is moved around two spaced-apart turning rollers 14. At least two of the sheets 1′ have dissimilar filtering characteristics. Such a sieve apparatus is known from e.g. applicant's granted patent NO 323519, wherein at least one suction nozzle is disposed up against a lower side of the endless sieve cloth for provision of a fluid flow through at least a portion of the material located on the endless sieve cloth, or from NO 326594 or patent application NO 20110438.

Hereinafter, the sheets 1′ of sieve cloth will also be termed sieve cloth sheet 1′.

FIG. 1 shows a sieve apparatus 10 of a type being sold under the trademark MudCub®, wherein an endless support belt 12 is disposed around two spaced-apart turning rollers 14 (only one shown in FIG. 1). It should be appreciated that the very support belt 12 may constitute a sieve cloth 1 capable of being used for sieving of relatively coarse particles.

FIG. 2 shows, in larger scale, detail A as depicted in FIG. 1. An attachment means 16 is connected to a portion of the support belt 12. In the embodiment shown, the attachment means 16 is releasably connected to the support belt 12 by means of a mounting bracket 16′ attached to the support belt 12 by means of a clip device. The object of the releasable mounting bracket 16′ will be explained in the following.

FIG. 3, FIG. 6 and FIG. 7 illustrate the manner in which a sieve cloth sheet 1′ is introduced in the sieve apparatus 10.

In FIG. 3, a first end portion 3 of the sieve cloth sheet 1′ is attached to a portion of the support belt 12 by means of an engagement means 4 brought into engagement with the attachment means 16 via an upwards projecting portion of the mounting bracket 16′. This is shown in larger scale in FIG. 4.

In the embodiment shown, the engagement means 4 and the attachment means 16 connected to the mounting bracket 16′ are complementary and may, for example, be comprised of a so-called hook and loop fastener, a magnet, push buttons or a similar releasable attachment device. The engagement means 4 may be the same as the cloth attachment means which, for practical reasons, will be denoted with the same reference numeral as that of the first end portion 3 of the sieve cloth sheet.

One of the advantages of the releasable mounting bracket 16′ is that it may be located at a desirable location in the support belt 12. For example, it will be appropriate for an operator to position the mounting bracket 16′ above the turning roller 14, which is located at an access hatch 11 (shown in an open state in FIG. 1). By so doing, there is no need for moving the support belt 14 to render the attachment means 16 for the sieve cloth sheet 1′ accessible.

FIG. 5 shows a front elevation, as viewed from above, of only the support belt 12 depicted in the sieve apparatus 10 of FIG. 1. In FIG. 5, the end portion 3 of the sieve cloth sheet 1′ is releasably attached to the attachment means 16, which is protruding upwards from the mounting bracket 16′. Thus, FIG. 5 shows the same as in FIG. 3, but seen from above. For the sake of clarity, a portion of the end portion 3 of the sieve cloth sheet 1′ is shown in a removed state. This is shown by means of a zigzag line.

In an alternative embodiment, it should be appreciated that the attachment means 16 shown in FIG. 3 may be fixedly connected to the support belt 12. In order to facilitate a desirable positioning of the attachment means 16 in context of fastening the sieve cloth sheet 1′ to the support belt 12, as shown in FIG. 3, the support belt 12 may be connected to a signal transmitter 20 (see FIG. 5) structured to communicate with a receiver 21 (see FIG. 2) connected to a control system (not shown), wherein the control system is structured in a manner allowing it to control a driving device 22 (see FIG. 1) for rotation of the turning roller 14, and in such a manner that the support belt 12 is brought to a stop in a position within which the attachment means 16 is located in a suitable position relative to e.g. the hatch 11 of the sieve apparatus 10. In FIG. 1, the hatch 11 is shown in a lowered position in a front portion of the sieve apparatus 10. The very control system, and the manner in which it controls the driving device 22, will be well known to a person skilled in the area and, for this reason, will not be described further in this document.

Even though the embodiment shown in FIG. 2 indicates that the attachment means 16 is comprised of a fastening spot, it should be appreciated that the attachment means 16 may just as well be comprised of a lengthy attachment means. Such a lengthy attachment means may be a ribbon extending, for example, parallel to the turning roller 14 extending between the side portions of the support belt 12. An attachment means of such a type may be continuous or consist of several individual elements. For example, and alternatively, transverse elements 15 may constitute an attachment means for a rope or a strip, as mentioned above.

Similar to the attachment means 16 shown in FIG. 2, a lengthy attachment means may be releasably connected to the support belt 12, for example by means of at least two mounting brackets 16′. As such, the attachment means 16 shown in FIG. 4 may be a ribbon.

FIG. 6 shows the first end portion 3 of the sieve cloth sheet 1′ upon being pulled over all of the at least two turning rollers 14 in the sieve apparatus 10 and almost back to its starting position, as shown in FIG. 3. This is achieved upon setting the turning roller 14 into rotation R by means of the driving device 22 depicted in FIG. 1.

In FIG. 7, the first end portion 3 of the sieve cloth sheet 1′ has been brought into engagement with a second end portion 5, and in such a manner that the sieve cloth sheet 1′ constitutes an endless sieve cloth 1. The cloth attachment means used to provide the connection is, for practical reasons, denoted with the same reference numeral as that of the first end portion 3 and the second end portion 5 of the sieve cloth sheet 1′. This has been carried out in all relevant figures.

In the embodiment shown in FIG. 3, FIG. 6 and FIG. 7, it is evident that the sieve cloth sheet 1′ is comprised of one piece. It should be appreciated, however, that the sieve cloth according to the present invention includes two or more sieve cloth sheets 1′ attached to each other in series, as shown in FIGS. 8 a, 8 b and 9 a. At least two of the sieve cloth sheets 1′ have dissimilar filtering characteristics.

In FIG. 8 a, three sieve cloth sheets 1′ arranged in series are shown. In the embodiment shown, each of the sieve cloth sheets 1′ has a filtering characteristic being dissimilar to the filtering characteristic of the two other sieve cloth sheets 1′. The end portions 3, 5 of each of the sieve cloth sheets 1′ extend in an arch form between the side portions 7 of the sieve cloth sheets 1′.

In FIG. 8 b, two sieve cloth sheets 1′ arranged in series are shown. The two sieve cloth sheets 1′ are shown as two sieve cloth sheets 1′ having dissimilar filtering characteristics. The end portions, hence the cloth attachment means 3, 5 of each of the sieve cloth sheets 1′, extend slantingly between the side portions 7 of the sieve cloth sheets 1′, i.e. at an angle different from 90° to the side portions 7 of the sieve cloth 1.

The purpose of arranging the end portions 3, 5 with an arch form and aslant, as shown in FIGS. 8 a and 8 b, respectively, is to prevent the joint of the end portions 3, 5 from being passed simultaneously over the transverse elements 15 of the support belt 12 (see FIG. 5). Tests have shown that if the transverse elements 15 exhibit a protrusion or a depression relative to the rest of the support belt 12, the transverse elements 15 may produce a certain resistance to relative movement between the sieve cloth 1 and the support belt 12. Such a resistance may cause said relative movement to become “jagged”, simultaneously allowing it to produce an undesirable load on the joint between two end portions 3, 5. Upon disposing the joint at an angle relative to the transverse elements 15 of the support belt, passing the joint simultaneously over all of the transverse elements 15 is avoided, whereby a “soft” relative movement is achieved.

FIG. 9 a shows, in perspective, a front elevation of two sieve cloth sheets 1′ arranged in series. The uppermost thereof is comprised of a waveformed sieve cloth sheet 1′. The waveform appears more clearly in FIG. 9 b, wherein detail C of FIG. 9 a is shown in larger scale.

The purpose of a waveformed sieve cloth is, among other things, to be able to increase the collective area of the filtering surface, thereby rendering it larger than the basic outline of the sieve cloth 1. Moreover, a waveform having ridges 2 and depressions 2′ will provide a resistance to flow excursions, transverse to the waves, of material being supplied to the sieve cloth. Thus, a sieve cloth having a waveform may also function as a form of flow rectifier, insofar as the supplied material will flow more readily within the depressions 2′ than across the ridges 2.

Another advantage of providing a sieve cloth sheet 1′ with a waveform, as shown, is that the sieve cloth sheet 1′, when passed over the turning roller 14 (shown in e.g. FIG. 1), more stretching will be produced in the ridges 2 of the sieve cloth sheet 1′ than in the depressions 2′ thereof. In the embodiment of the sieve cloth sheet 1′ shown at the top of FIG. 9 a, the ridges 2 and the depressions 2′ extend parallel to the turning rollers 14. The distance between two ridges 2 located side by side will increase when said ridges 2 pass the turning roller 14. Material located in the depression 2′ between said two ridges 2 may thus be able to disengage more readily from the sieve cloth sheet 1′ and fall off when the upper side of the sieve cloth sheet 1′ is facing downwards upon having been passed over the turning roller 14, which is located downstream of a material supply portion in the sieve apparatus 10. If the ridges 2 and the depressions 2′ extend parallel to the direction of movement of the sieve cloth sheet 1′, the ridges 2 will be pulled down somewhat when the sieve cloth sheet 1′ passes over the turning roller 14. Tests have shown that also this has a positive impact on the “cleaning” of the sieve cloth sheet 1′.

In FIGS. 10 a and 10 b, an alternative embodiment of a sieve cloth sheet 1′ having a surface area or sieve area being larger than the basic outline of the sieve cloth sheet 1′ is shown. In the embodiment, which is shown at best in FIG. 10 b, the sieve cloth is formed with a plurality of dome-shaped bulbs 2 protruding upwards from a base 2′. It should be appreciated that both the base 2′ and the bulbs 2 are formed from sieve cloth material. The advantages of the bulbs 2 are the same as those of the sieve cloth sheet 1′ shown in FIG. 9 b, at least with respect to cleaning and limited flow excursions of supplied material.

The first end portion 3 and the second end portion 5 of a sieve cloth sheet 1′ are, as mentioned, provided with a first attachment means and a second attachment means, respectively. The attachment means may be fastening spots, or “ribbons” of the attachment means extending completely or partially along the end portions 3, 5.

Upon connecting an attachment means corresponding to the first attachment means to one of the side surfaces 7 of the sieve cloth sheet 1′, and also connecting an attachment means corresponding to the second attachment means to the opposite side surface 7, the sieve cloth sheet 1′ may be rotated 90° relative to the longitudinal direction of the sieve cloth 1. This, of course, presupposes that the sieve cloth sheet has a square shape, or that the end portions 3, 5 are provided in an elastic material. For example, the wave direction of the sieve cloth sheet 1′ shown at the top of FIG. 9 a may thus be changed from extending parallel to the turning rollers 14 to extending perpendicular to the turning rollers 14.

The end portions 3, 5 of the sieve cloth sheets 1′ may be provided with a cloth attachment means at both the lower side and the upper side of the sieve cloth sheet 1′. By so doing, a sieve cloth sheet 1′ may be formed as a multilayer sieve cloth sheet, wherein the layers are arranged in a sandwich structure. For example, the middle sieve cloth sheet 1′ of FIG. 8 a may be comprised of one layer of sieve cloth, whereas the lowermost sieve cloth sheet 1′ of FIG. 8 a may be comprised of a sieve cloth sheet 1′ corresponding to the middle sheet, but having a further sieve cloth sheet 1′ disposed on-top thereof.

As such, the filtering characteristic of the individual sieve cloth sheet 1′ may be changed to a finer filtration, and/or the effective life properties of the individual sieve cloth sheet 1′ may be changed without having to remove the sieve cloth sheet 1′ bearing against the support belt 12.

In one embodiment, a sieve cloth sheet 1′ having a first longitudinal extent is structured in a manner allowing it to receive, at the upper side thereof, a second sieve cloth sheet 1′ having a second extent. In one variant, the second extent is less than the first extent. In another variant, the second extent is larger than the first extent.

In FIG. 9 a, dividing profiles 30 protruding upwards from a portion of the lowermost of the two sieve cloth sheets 1′ is shown. The main objective of the dividing profiles 30 is to provide a flow restriction in order to reduce the flow of supplied material from one sieve cloth sheet 1′ onto a subsequent sieve cloth sheet. The material being supplied may include a cleaning-promoting material, for example water, steam, air and/or a detergent or a solvent.

In the embodiment shown, two of the dividing profiles 30 are arranged substantially parallel to the direction of movement of the sieve cloth, as indicated with arrows M in FIG. 9 a, whereas the other two dividing profiles 30 shown are arranged substantially perpendicular to the direction of movement M of the sieve cloth. It should be appreciated, however, that the number of dividing profiles may differ from the four shown. It should also be appreciated that one or more dividing profiles may be disposed aslant relative to the direction of movement of the sieve cloth in the sieve apparatus.

In order also to allow those of the dividing profiles 30 being arranged non-parallel to the turning rollers 14 of the sieve apparatus 10 to be passed around the turning rollers 14, the dividing profiles 30 are provided in a flexible material, wherein the portion of the dividing profiles 30 facing furthest away from the sieve cloth sheet 1′ is stretched more than the portion located closest to a turning roller 14 upon passing thereof. The dividing profiles 30 may also be formed in such a manner that, upon passing the turning rollers 14, they bend laterally and down toward the sieve cloth sheet 1′, and then come upright upon passing thereof. Alternatively or additionally, the dividing profiles 30 may be provided with a plurality of slots 30′ allowing the dividing profiles to be bent around the turning rollers 14.

In the embodiment shown, said subsequent sieve cloth sheet may be a further sieve cloth sheet (not shown), or it may be the waveshaped sieve cloth sheet 1′ upon having connected the first end portion 3 thereof together with the second end portion 5 of the lowermost sieve cloth sheet 1′ by means of said first attachment means and second attachment means.

It should be appreciated that one or more dividing profiles 30 may be disposed at any location on any sieve cloth sheet 1′, and at any angle relative to the direction of movement of the sieve cloth sheet 1′, and at any extent. If the dividing profiles 30 extend non-parallel to the turning rollers 14, the dividing profiles 14 must be made of an elastic material capable of being passed around the turning rollers 14, or the dividing profile 30 must be provided as a series of individual elements.

The object of providing an endless sieve cloth 1 comprising at least two sieve cloth sheets 1′, wherein at least two of the sieve cloth sheets 1′ have dissimilar filtering characteristics, are as follows. Upon recovery of e.g. drilling mud, it is desirable for the mud to satisfy specific properties with respect to, among other things, specific gravity and a grading curve for the material fines being admitted through the sieve cloth. Upon monitoring the properties of the drilling mud recovered by means of the sieve apparatus 10, the distribution of e.g. the fines content in the drilling mud may be adjusted so as to optimize the sieving operation without having to remove the sieve cloth 1 from the sieve apparatus 10 in order to replace it with a new one having a different filtering characteristic. This is achieved by allowing the particular one of the sieve cloth sheets 1′ having the desirable filtering properties, to receive the material to be sieved, and allowing this sieve cloth sheet 1′ to undergo a back-and-forth motion, instead of allowing the endless sieve cloth to rotate in one direction only in the sieve apparatus 10. Optionally, the sieve cloth may be moved in one direction, but upon adjusting the velocity in accordance with the particular sieve cloth sheet 1′ receiving the material, the sieving operation may be optimized.

Even though each of the sieve cloth sheets 1′ shown in FIGS. 8 a, 8 b and 9 a are depicted having dissimilar filtering characteristics, it should be appreciated that two or more sieve cloth sheets 1′ may have the same filtering characteristic in an alternative embodiment. If damage occurs to one of the sieve cloth sheets 1′, the object of such a solution is, among other things, to avoid having to replace the entire endless sieve cloth with a new one, but only to replace the sieve cloth sheet 1′ being damaged.

The sieve cloth sheets 1′ shown in FIGS. 8 a, 8 b and 9 a may be attached to each other in order to provide one sieve cloth sheet prior to attaching the sheet to the support belt 12, as shown in FIG. 3. However, the joining of the sieve cloth sheets 1′ may be carried out simultaneous with the introduction of the sieve cloth sheet 1′ in the sieve apparatus 10. This, for example, may be carried out by attaching a first sieve cloth sheet to the attachment means 16 of the support belt 12, moving it a distance into the sieve apparatus 10 by rotating the turning roller 14, and attaching the first end portion 3 of a second sieve cloth sheet to the second end portion 5 of the first sieve cloth sheet 1′. This is repeated, possibly with a further sieve cloth sheet, until an endless sieve cloth 1 may be provided, as explained and shown in FIG. 7.

In order to facilitate control of the apparatus, the support belt 12 is provided with a signal transmitter 20, as discussed earlier. Furthermore, one, several or all of the sieve cloth sheets 1′ may be provided with a signal transmitter 19, as shown in FIG. 8 a. The purpose of said signal transmitter 19 is to allow the driving device 22 to be controlled for rotation of the turning roller 14, and in such a manner that a desirable portion of the endless sieve cloth 1, for example a specific sieve cloth sheet 1′, is brought to a stop when in a desirable position. Moreover, the signal transmitters 19 in so each of the sieve cloth sheets 1′ are used in context of controlling said optimization of the sieving operation.

The wear of the sieve cloth is affected by the velocity difference between the sieve cloth 1 and the support belt 12. Upon providing the support belt 12 and at least one of the at least one sieve cloth sheet 1′ with a signal transmitter 19, 20, the velocity difference between the support belt 12 and the sieve cloth 1 may be measured. This, in turn, may be used to control the rotational velocity of the turning roller 14, whereby an optimum velocity difference is achieved.

In a preferred embodiment, the signal transmitter 19, 20 is a so-called RFID-chip and the receiver is an RFID-transceiver, both of which are based on well-known and thoroughly tested technology which will be known to a person skilled in the area and, hence, will not be discussed in further detail in this document. For example, the signal transmitter 19, 20 may be connected to a portion of the sieve cloth sheet 1′ and the support belt 12, respectively, as discussed in applicant's Norwegian patent application 20110438. 

1. A method of controlling separation of solid particles from a fluid, wherein the separation is carried out by means of a sieve apparatus (10) which includes an endless sieve cloth (1) structured in a manner to rotate around at least two spaced-apart turning rollers (14), the method comprises: arranging at least two sieve cloth sheets (1′) in series in a direction of movement of the sieve cloth (1), wherein at least two of the at least two sieve cloth sheets (1′) have dissimilar filtering characteristics; and controlling the endless sieve cloth (1) by adjusting the direction of rotation and speed of rotation of the turning rollers (14) in such a manner that a desirable amount of solid particles and fluid is supplied to at least one, or is distributed between two or more, of the at least two sieve cloth sheets having a desirable filtering characteristics.
 2. The method according to claim 1, wherein the method further includes the step of providing the sieve cloth sheets (1′) with a signal transmitter (19) to communicate with a receiver (21) connected to a control system for controlling a driving device (22) for rotation of at least one of the turning rollers (14).
 3. The method according to claim 2, wherein the method further comprises allowing a desirable portion of the sieve cloth to be brought to a stop in a predetermined position in the sieve apparatus.
 4. The method according to claim 1, wherein the sieve cloth (1) is of a type being supported by a support belt (12) bearing against the turning rollers (14), wherein the method further includes the following steps: bringing at least a portion of at least one of the sieve cloth sheets (1′) into engagement with a portion of the support belt (12); positioning the sieve cloth sheet (1′) against the support belt (12) by moving the support belt (12) around the turning rollers (14); and bringing at least two adjoining end portions (3, 5) of the sieve cloth sheets (1′) into engagement with each other until the at least two sieve cloth sheets (1′) form an endless sieve cloth (1).
 5. The method according to claim 4, wherein the method further comprises releasing the sieve cloth from said engagement with the support belt (12).
 6. The method according to claim 5, wherein the step of releasing the sieve cloth (1) from engagement with the support belt (12) is an active step on behalf of an operator.
 7. The method according to claim 5, wherein the step of releasing the sieve cloth (1) from engagement with the support belt (12) occurs in response to an engagement having a strength being less than a force arising between the support belt (12) and the endless sieve cloth (1) when both are set in motion around the turning rollers (14).
 8. The method according to claim 3, wherein engagement between the sieve cloth (1) and the support belt (12) is provided by means of an attachment means (16, 16′) releasably connected to a portion of the support belt (12).
 9. The method according to claim 3, wherein the method further comprises connecting at least one signal transmitter (20) to a portion of the support belt (12); putting the at least one signal transmitter (20) into communication with a receiver (21) connected to a control system, wherein the control system is structured to control a driving device (22) providing rotation of the support belt (12), and in such a manner that the driving device (22) is brought to a stop when the signal transmitter (20) is located in a predetermined position in the sieve apparatus (10).
 10. The method according to claim 9, wherein the at least one signal transmitter (20) is releasably connected to a portion of the support belt (12).
 11. A sieve apparatus (10) for separating solid particles from a fluid, wherein the sieve apparatus (10) is of a type provided with an endless sieve cloth (1) to be moved around two spaced-apart turning rollers (14), the sieve cloth (1) comprises: at least two sieve cloth sheets (1′) arranged in series in a direction of movement of the sieve cloth (1), and wherein at least two of the at least two sieve cloth sheets (1′) have dissimilar filtering characteristics; and a control means for adjusting a direction of rotation and a speed of rotation of the turning rollers (14) to allow sieve cloth sheets (1′) having a desired filtering characteristic to receive the solid particles and fluid to be sieved.
 12. The sieve apparatus according to claim 11, wherein at least one of the sieve cloth sheets (1′) has a square shape with a width being equal to a length.
 13. The sieve apparatus according to claim 11, wherein a size, in a longitudinal direction, of at least some of the openings of the cloth is dissimilar to the size, in a widthwise direction, of at least some of the openings of the cloth.
 14. The sieve apparatus according to claim 11, wherein a surface area of at least one of the sieve cloth sheets (1′) is larger than a basic outline of the sieve cloth sheet (1′), the outline of which is defined by the extent of the cloth in a longitudinal direction and in a widthwise direction.
 15. The sieve apparatus according to claim 11, wherein at least one of the sieve cloth sheets (1′) is provided with one or more dividing profiles.
 16. A drilling rig for use in context of drilling a well for recovery of petroleum, wherein the drilling rig includes a sieve apparatus (10) for cleaning drilling mud, wherein the sieve apparatus (10) includes the sieve cloth (1) according to claim
 11. 